The present invention relates to offshore platforms and, especially, to the assembly of an offshore platform by mating a pre-constructed integral deck portion being carried by a barge, or the like, onto a jacket portion that is already positioned with its base secured to the bed of a sea or other body of water and its top at, or slightly above, water level. Throughout this specification, the term "jacket portion" is used without limitation as to the material or manner of construction of the jacket portion.
The invention is especially applicable where the jacket portion is standing secured to the sea bed, or the like, in comparatively deep water or is floating with its top at, or slightly above, water level, and a deck portion in the form of a pre-constructed integrated deck structure is to be lowered onto it from a barge, or the like.
Viewed from one aspect, the present invention provides a combination of a deck portion and a base portion for an offshore platform, including one or more mating devices, each of which comprises an extendable stabbing pin mounted on one of said portions and a capture member for said stabbing pin mounted on the other of said portions, and resilient means associated with each of said mating devices and arranged to oppose a reduction in the separation of the said portions following operation of its associated mating device, the said resilient means of a first one of said mating devices having a smaller spring rate than that of a second resilient means mounted on the same or a different mating device, and the first and second resilient means being arranged to become effective in that order upon operation of the said mating device(s), whereby the said reduction in the separation of the said portions upon operation of the mating device(s) is opposed by the said resilient means with a spring rate which increases as the separation decreases.
In a first embodiment, each of the tubular leg members has the leg mating system described above comprising a first soft spring means and a second harder spring means. In an alternate embodiment, the four corner leg members contain the soft spring means, while some or each of the intermediate leg members contain the harder spring means.
Viewed from another aspect, the invention provides a method of assembling an offshore platform by mating a deck portion to a base portion, which comprises operating a plurality of mating devices by, in each case, extending a stabbing pin from one of said portions to engage a capture member on the other of said portions, and reducing the separation between the said portions against forces exerted by resilient means associated with each of said mating devices, the spring rate of the said resilient means of a first one of said devices being smaller than that of a second resilient means mounted on the same or on a second such device, the first and second resilient means being arranged to become effective in that order upon operation of the said mating devices, whereby the said reduction in the separation of the said portions upon operation of the mating devices is opposed by the said resilient means with a spring rate which increases as the separation decreases.
In the above-mentioned second embodiment, a plurality of mating devices with said first spring rate, preferably the corner legs, and a separate plurality of mating devices with said second spring rate, preferably the intermediate legs, are provided. In operation, all of the first mating devices will then be operated (not necessarily simultaneously) before any of the second mating devices are operated.
Viewed from a further aspect, the invention provides a combination of a deck portion and a base portion for an offshore platform, including a plurality of mating devices each of which comprises an extendable stabbing pin mounted on one of the said portions and a capture member for said stabbing pin mounted on the other of the said portions, and resilient means in said mating devices arranged, during operation of said devices, to oppose a reduction in the separation of the said portions with a total spring rate that is greater at small separations than at large separations.
Viewed from yet another aspect, the invention provides a method of assembling an offshore platform by mating a deck portion to a base portion, which comprises operating a plurality of mating devices by extending stabbing pins from one of said portions to engage respective capture members on the other of said portions, and reducing the separation between the deck portion and the base portion against a force exerted by resilient means associated with said mating devices, the total spring rate of the said resilient means being greater at small separations than at large separations.
With suitable arrangement of the mating devices the stabbing pins can be extended into engagement with their capture members and then serve to guide the deck portion into correct mating alignment as it is lowered onto the base portion, while the increasing spring rate of the said resilient means ensures a smooth transfer of the weight of the deck portion from the barge onto the base portion.
Preferably the stabbing pins are mounted on the deck portion and the capture members on the base portion.
A distal end portion of each stabbing pin and a corresponding portion of its associated capture member may be so shaped as to tend to produce a self-centering action. The distal end portion of the stabbing pin is advantageously convex and the corresponding portion of the capture member concave, and they preferably have conical surfaces.
The said deck portion and base portion may include tubular leg members that are arranged to abut end to end when the said portions are fully mated, and each said mating device is then advantageously disposed within a said leg member of the base portion and the corresponding leg member of the deck portion. Preferably, when the stabbing pin is retracted the mating device lies completely within the space envelope of the two legs, where it will neither be exposed to accidental damage nor obstruct other operations carried out within the vicinity of either the deck portion or the base portion.
The invention also provides a platform assembled from a combination of a deck portion and a base portion according to the invention and/or by a method according to the invention.
The invention further provides a mating device for a combination according to the invention, and a set of parts of such a mating device.
Various other features, characteristics and advantages of the present invention will become apparent after a reading of the following specification.